A vehicle fuel tank is vented to allow vapors to move in and out of the tank in order to keep internal pressure in the tank about equal to atmospheric pressure as fuel is drawn from the tank and as internal gas pressures build up.
To reduce atmospheric emissions of fuel, vented vapors may be channeled via a back pressure control valve to a charcoal canister which absorbs and temporarily traps fuel vapor. On restarting the engine, filtered air flows through the canister and carries the fuel vapor away to be burned in the engine. The back pressure valve is used to prevent "trickle filling" of the fuel tank.
The venting system typically comprises two vent ports, one on either side of the top of the fuel tank, both of which are connected to a back pressure valve by pipes. The back pressure valve is in turn connected to a charcoal canister. To prevent fuel from spilling out of the tank in the event of the vehicle turning over or banking steeply, each vent port is provided with a rollover valve ("ROV") which is welded to the tank or mounted by means of a grommet.
A problem with such venting systems is that there are quite a number of places where leakage to atmosphere may occur, namely between each ROV and the tank, between each valve outlet and a pipe, and between each pipe and the back pressure valve. The cost of sophisticated connections to various components is high.
It is an object of the present invention to reduce the above problem.